In the 3rd Generation Partnership Project (3GPP) which is the standardization group for a mobile communication system, the specification work of evolved packet system (EPS) described in NPL 1 as the next generation mobile communication system has progressed, and a wireless LAN (WLAN) as well as Long Term Evolution (LTE) as an access system connected to the EPS has been examined.
In the 3GPP, as described in NPL 2, proximity services (ProSe) of notifying user equipment (UE) of the presence of another user equipment in proximity have been examined. In the ProSe, the UE directly performs the transmission and reception of data by establishing a direct communication path with the UE in proximity without using a base station.
In the ProSe, in order to perform the transmission and reception of data between the UEs, the transmission and reception of data can be performed without using an access network based on an access technology such as LTE or a mobile communication network such as a core network, and thus, an offload effect of avoiding traffic concentration is expected.
In the ProSe, the use of two methods as a direct communication path between the UEs has been examined. The first method is a method (hereinafter, referred to as LTE Direct) of establishing the direct communication path between the UEs using an LTE access technology, and the second method is a method of establishing the direct communication path using a wireless LAN access technology.
In the LTE Direct, the UE uses a commercial frequency allocated in an LTE system of each mobile communication provider, and directly transmits and receives data to and from another UE by using an LTE communication system.
In the WLAN Direct, the UE uses a non-commercial frequency allocated in the WLAN, and directly transmits and receives data to and from another UE.
In the ProSe, the necessity for the UE to detect the presence of a communication target UE in proximity by discovering the communication target UE in order to transmit and receive data through the LTE Direct or the WLAN Direct is given as a service request condition.
In the ProSe, it has been examined that any one of the UEs that perform direct communication is connected to another UE by establishing a direct communication path with another UE and is connected to a base station disposed in an access network of the related art.
The UE connected to the base station is connected to the core network via the base station to establish the communication path. It has been examined that the UE connected to the base station relays the direct communication path with the other UE and the communication network with the core network. In the relaying of the ProSe, the UE that has established the direct communication path and has established the communication path by being connected to the core network has a function of receiving transmission data of the UE connected through the direct communication path and delivering the data to the core network. This UE has a relay function of receiving data delivered from the communication path connected to the core network and transmitting the data to the UE connected to the direct communication path through the direct communication path.
As stated above, the ProSe is used to provide a service of notifying a certain UE of the presence of a UE in proximity, a service of providing communication through the direct communication path between the UEs, and the relay function of the UE.